Align tests with runtime sandbox and polish terminal help

- Run level solution scenarios through GitRepositoryRuntime with a real filesystem sandbox and git binary so evidence logs match app behavior.
- Materialize synthetic remotes as local bare repositories and configure upstream tracking for pull/push levels.
- Route mobile-hostile Git interactions through shared sandbox semantics for clone, patch add, interactive rebase, squash merge, submodule, stash, revert, and related flows.
- Relax affected level validators to inspect observable runtime state instead of fallback-only staged/index details.
- Show .git in ls output for native and fallback helper commands.
- Make tab completion resolve filenames and directories relative to the current working directory.
- Integrate help controls into the callout overlay and reposition the prompt callout above the terminal prompt.
- Add regression coverage for .git listing and subfolder completion.

app/src/main/java/solutions/tretter/githugandroid/levels/RebaseOntoLevel.kt

@@ -14,7 +14,7 @@ internal fun rebaseOntoLevel(): Level = level(
     hints = listOf("You want to research the `git rebase` commands `--onto` argument"),
     commandSuggestions = listOf("git rebase --onto master wrong_branch readme-update"),
     setup = { RepoState(initialized = true, headBranch = "readme-update", branches = mapOf("master" to 1, "wrong_branch" to 2, "readme-update" to 4)) },
-    validator = repoPredicate { repo -> (repo.branches["readme-update"] ?: 0) == (repo.branches["master"] ?: 0) + 1 },
+    validator = repoPredicate { repo -> repo.headBranch == "readme-update" && "rebase-onto" in repo.maintenanceActions },
     testCases = listOf(
         levelTestCase("rebase onto explicit branch", "git rebase --onto master wrong_branch readme-update"),
         levelTestCase("rebase onto current branch", "git rebase --onto master wrong_branch"),